the sound accompanying heart function. Occurring at regular intervals during specific phases of the cardiac cycle, heart sounds are rapid aperiodic sound oscillations.

Two basic heart sounds are distinguished during auscultation of the heart and phonocardiography. The first sound, which occurs at the beginning of the systole, is caused by myocardial tension, valve function, and the vibration of the walls of major vessels. The second sound occurs with the closure of the semilunar valves at the beginning of the diastole. A physiological third sound is often detected in children and adolescents.

A change in the nature or number of heart sounds, such as the occurrence of palpitations, may indicate the development of heart failure or the existence of heart disease or certain other afflictions.